Re: Which would you use?
- From: "Arny Krueger" <arnyk@xxxxxxxxxx>
- Date: Tue, 23 May 2006 08:45:53 -0400
"Ben Bradley" <ben_nospam_bradley@xxxxxxxxxxxxxxx> wrote in
message news:24vr62dtl8ik5hn8i7vld0qo7pn0430rdb@xxxxxxx
I was given a quad receiver about 20 years ago that had
four STK modules, and it always sounded nociably worse
than a lower-power stereo amp I had (I've never claimed
to have golden ears, so it must have been really bad to
bother me). I wish I had kept it just for the discrete
quad LP decoder circuitry. And to measure the power amp
distortion products.
Googling "darlington power pack" brings up pages with
various STK power amp modules. I looked up models
STK-0050 and STK-0080 that go by this name, and they're
not even a complete power amp. It's a complementary
emitter-follower output stage with each 'output'
transistor' being a Darlington-wired pair, and a fifth
transistor for bias with appropriate diodes and
resistors. FWIW, here's a couple data sheets with
schematics:
http://pdf1.alldatasheet.net/datasheet-pdf/view/82964/ETC/STK-0050.html
http://pdf1.alldatasheet.net/datasheet-pdf/view/41476/SANYO/STK-0080.html
Conceptually, this seems like a great idea for biasing
to have all the temperature-dependent components track
temperature-wise. I can only wonder how they messed up
the design of these things to make them sound bad.
Perhaps a designer actually got it right, but the
manufacturing cost pressures Muntzed it.
AFAIK the history of the STK modules is that in the late 1960s the Japanese
Ministry of International Trade and Industry (MITI) poured millions of
dollars into the development of a standardized solid state stereo receiver.
The various subsystems of the stereo receiver were assigned to various
manufacturers who had recognized expertise with that area of circuit
development. For example, the FM section might have been assigned to Kenwood
(Trio). My recollection is that Sanken were assigned the power amplifier.
Apparently, MITI repeated this process to expedite the development of a
consumer HDTV receiver, which is now considered to be a failure. I can't
find any evaluations of the earlier effort, no doubt due to the time that
has elapsed.
Most Japanese stereo receivers sold in the US during the 1970s contained
some of the fruit of MITI's efforts.
I recall a semi-honest mark of "quality" was "Discrete Output
Stage" meaning the power amplifier used individual output transistors
instead of these power module things.
I've seen the use of discrete output stage transistors touted in sales
literature as recently as just a few years ago. Apparently the Sanken
modules left a bad taste in many people's mouths. I would sincerily hope
that in the past 40 years, the industry has corrected the problem.
.
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